This invention is related to laser devices and is more particularly concerned with a new and improved construction whereby erbium laser rods are held within an imaging cavity in a manner such that masking of the rod does not occur.
Trivalent erbium ions when disposed in a glassy host material characteristically emit laser energy at a wavelength of approximately 1.54 nanometers. One distinct advantage which inures to the operation of an erbium doped laser device is that the human eye is quite absorbent to energy at this wavelength; therefore, natural protection against burning of the retina is inherent in the use of this device. The danger of retinal burn is less severe than with nearly all other known laser materials.
In spite of the foregoing important advantage, several disadvantages have been associated with laser devices utilizing erbium as the active laser ion therein. One of these disadvantages is that the erbium laser ion operates as a so-called "three level system". By this one means that the radiative transition from the high energy metastable level is directly to the ground state for the erbium laser ion. In a so-called "four level system", such as neodymium, the radiative transition occurs between the metastable state and another energy level which is above the ground state for that ion. Thereafter, a non-radiative transition occurs during which the laser ion returns to the ground level. As a result, the erbium laser active ions in the material when in the ground state are absorbent to laser energy at the emission wavelength of the laser. Therefore, unless one excites the trivalent erbium ions in the laser rod out of the ground state, a lossy condition exists within the laser rod. This prevents the laser from being operated at reasonable efficiencies.
This problem is particularly acute at those locations along the laser rod at which the laser rod is held by some member to position it within the surrounding imaging cavity. At these locations, the laser rod is masked from the pumping light energy. The erbium active laser ions under the holding members do not see the pumping light energy and are, therefore, allowed to remain in the ground state. When the energy emitted by the excited ions attempts to propagate through the masked areas of the laser rod, the unexcited ions under the holding members absorb some or all of this energy thereby at least greatly reducing the gain attributable to the laser rod.